Segment, flight, Airport

I've three classes Segement, Flight and Airport. Segment class holds origin and destination airport. Flight has other details like flight number, capacity, total price etc. Now i'm confused where to link airport to (segement or flight). Logically speaking it should link to Segement.

But i have one more class City which is linkedto airport indicating the cities an airport serves.

With this, if i link segment and airport together, then a segment is serving a city rather than the flight (which may have one or more segments).

Please clarify where should i link airport to - either segment or flight.